Bug 29811: Add timestamp option on authority record type

Bug 29811: Add timestamp option on authority record type

According to the timestamp option for bibs record type I added the
timestamp option for authority records.
Timestamp is already present in database on field "modification_time"

Test Plan :
1 - Be sure to have authority record type for easiest test create one
2 - Execute script export_records.pl in your koha/misc directory and
choose a date (example yesterday if you just created an authority
right now).(see export_records.pl -h for help)
3 - Timestamp option has no effect on authority record type
4 - Execute script again but choose the date of tomorrow for example
5 - Same result
6 - Apply this patch
7 - Play again steps 2 and 4
8 - On step 2 you will see only your authorities created today (because
script show you authority has changes since the date you choose in
option) and for step 4 you must see an empty file.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 24ee60cb62cfbe5dc80bbb698eb6fa1e99d1cd4e)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>